In an injection molding for injecting and filling a resin into a cavity inside a mold from a gate, where the cavity shape is complicated geometrically, a technique is used for providing a plurality of gates and feeding resins into the cavity from the individual gates so that the resins can be delivered into corners of the cavity. Where the resins are caused to converge from the plurality of gates as described above, a groove which is called a weld occurs on the surface of a shaped article at the converged portion of the resins. This causes the disfigurement of the shaped article.
As means for preventing occurrence of the weld, there has been so far proposed a resin injection molding method in which a mold is heated to raise a mold temperature on injection and filling of a resin to a temperature greater than or equal to a glass transition temperature and a heat distortion temperature where the resin is non-crystalline, and to a temperature greater than or equal to the melting point where the resin is crystalline (for example, refer to Patent Document 1). According to the above-described injection molding method, since resins converge at a converged portion in a molten state which is higher in temperature, the resins are solidified in such a state to be sufficiently pressed to the mold. Thereby, the groove depth of the weld can be completely eliminated at the converged portion. Alternatively, the weld can be made shallow so as to suppress the appearance thereof.